Intelligent transport systems (hereafter referred to as “ITS”) have been conceived and have started to be realized; the ITS is a new transport system configured to use a short range communication system called DSRC (Dedicated Short Range Communication; hereafter referred to as “DSRC”) to solve road traffic problems such as traffic accidents and traffic jams. In the ITS, roadside apparatuses installed on a road broadcast information to vehicle-mounted devices mounted in vehicles. Each vehicle-mounted device provides traffic information received from the roadside apparatus to an occupant in the vehicle in the form of voice, still images, or text data at predetermined timings. Attempts have been made to configure roadside apparatuses used in the ITS such that the apparatuses provide vehicle-mounted devices with information varying between the inbound lane and outbound lane of the road. If such information varying between the inbound lane and the outbound lane is provided, traffic information for the inbound lane transmitted by the roadside apparatus may be received by a vehicle-mounted device mounted in a vehicle traveling in the outbound lane, because of leakage, irregular reflection, or the like of electric waves to output the traffic information. In a known technique to solve such a problem, an electric wave absorber is provided at a tollgate on a toll road; the electric wave absorber enables inhibition of the leakage, irregular reflection, or the like of electric waves transmitted by the roadside apparatus (see Patent Document 1).
Patent Document 1: Japanese Patent Application Laid-Open No. 2002-237719 (FIG. 1 and the like)